Process for producing fine fibrous structures

ABSTRACT

An aqueous disperse system, preferably an aqueous emulsion, comprising a molten linear polymer droplets dispersed in the aqueous phase and containing a fine water-sorption agent and a positive solvent with respect to the polymer is ejected from a high-pressure region at a temperature above the polymer melting point and below the critical temperature of the disperse system and at a pressure above the saturated vapor pressure of the disperse system into a low-pressure region at a temperature and pressure permitting evaporation of a liquid phase within the disperse system thereby to produce a fine fibrous structure of the polymer.

United States Patent [1 1 Ueki et al.

[4 Oct. 21, 1975 [54] PROCESS FOR PRODUCING F1NE FIBROUS STRUCTURES [75]Inventors: Shiro Ueki; Yoshimitsu Miyata, both of Yokkaichi, Japan [73]Assignee: Kabushiki Kaisha Oki Yuka Goeishi Kenkyujo, Tokyo, Japan [22]Filed: Sept. 20, 1973 [21] Appl. No.: 399,138

Related US. Application Data [63] Continuation of Ser. No. 182,524,Sept. 21, 1971,

abandoned.

[30] Foreign Application Priority Data Sept. 25, 1970 Japan 45-83937[56] References Cited UNITED STATES PATENTS 3,377,323 4/1968 loka et al.260/75 T 3,402,231 9/1968 Bynum et al. 264/210 F 3,431,242 3/1969 Waterset al. 260/78 S 3,432,483 3/1969 Peoples et al. 260/78 S 3,449,2916/1969 Lerman et al.... 260/29.6 NR 3,472,801 10/1969 Lerman et al.264/5 3,481,906 12/1969 Marayama et al 260/78 S 3,542,715 11/1970 Whiteet al. 260/2.5 3,560,425 2/1971 Wolinski 260/29.6 AN 3,770,663 11/1973Ueki et al 260/2.5 B 3,770,856 11/1973 Ueki et a1. 264/205 3,774,38711/1973 Woodell 57/140 R 3,808,091 4/1974 Hoki et al. 162/157 R PrimaryExaminer-Jay H. Woo Attorney, Agent, or Firm-Wenderoth, Lind & Ponack [57] ABSTRACT An aqueous disperse system, preferably an aqueous emulsion,comprising a molten linear polymer droplets dispersed in the aqueousphase and containing a fine water-sorption agent and a positive solventwith respect to the polymer is ejected from a high-pressure region at atemperatureabove the polymer melting point and below the criticaltemperature of the disperse system and at a pressure above the saturatedvapor pressure of the disperse system into a lowpressure region at atemperature and pressure permitting evaporation of a liquid phase withinthe disperse system thereby to produce a fine fibrous structure of thepolymer.

13 Claims, No Drawings PROCESS FOR PRODUCING FINE FIBROUS STRUCTURESThis is a continuation of application Ser. No. 182,524, filed Sept. 21,1971, and now abandoned.

BACKGROUND This invention relates generally to techniques in theproduction of fine fibrous structures and more particularly to a newprocess for producing fibrous structures for providing fine fiberssuitable for use in making synthetic papers.

Papers of a structure wherein fibers are in intertwined state are knownas one class of synthetic paper. A paper of this class is made throughthe use of fibers of a synthetic polymer as one constituent of a naturalcellulosic paper-making material or as the predominant paper-makingmaterial.

One advantageous feature of a synthetic paper of this class is that itsstructure is substantially the same as that of conventional orcellulosic papers. However, fibers for synthetic papers are required tohave a high degree of molecular orientation, to be thin, and to have ahighly fibrillated structure, and difficulties are encountered inadapting synthetic polymeric fibers of the type which have beengenerally used for fabrics and clothing to fulfill these requirements.Furthermore, synthetic polymeric fibers of this general character aredeficient in hydrophilic property. For these reasons, satisfactorysynthetic papers of this class have not been available.

On one hand, there is a known method for producing fine fibers usable inmaking synthetic papers of this class which comprises abruptly jettingor ejecting a solution of a crystalline polymer under pressure and at atemperature above room temperature through orifices into a low-pressureregion and thereby reproducing the polymer as a fine fibrous structuresimultaneously with the resulting evaporation of the solvent used.

By macerating or beating the fine fibrous structure thus obtained bythis spinning method, fine fibers of tibrillated structure having amplefineness and ample strength due to molecular orientation can beproduced. When these fine fibers are used in paper making, syntheticpapers even more closely resembling conventional paper can be produced.

Fine fibers of this character and the method for producing the same,however, cannot be said to be entirely free of problems. Morespecifically, for example, the choice of a usuable solvent is limitedsince this solvent must have a low boiling point and, moreover, must beused in a large quantity. Furthermore, fine fibers produced in thismanner lack hydrophilic property and, consequently, cannot be easilyused in paper making.

SUMMARY It is an object of this invention to provide a relatively simpleprocess for producing fine fibrous structures wherein the abovedescribed difficulties and problems are overcome. We have found thatthis object can be achieved by ejecting an aqueous dispersion ordisperse system of a molten linear polymer droplets dispersed in theaqueous phase under pressure into a low-pressure region.

In the production of fine fibers by diminution of mass of polymer, thefine fibers can be produced by dispersing blowing agent in the polymermass and subjecting the blowing agent-containing polymer mass to a lowerpressure to allow the expansion of the blowing agent thereby to splitthe polymer mass into fine fibers. For this, it is the most important toemploy a blowing agent having a large expansion capacity and to dispersethe blowing agent in a polymer mass finely enough to split the polymermass to desired fine fibers.

Further, in order to obtain a molecularly oriented polymer, it isdesirable to finely-disperse a large amount of blowing agent which has alarge expansion capacity in the polymer mass and improved wettability atthe interface between the blowing agent and the polymer, and to quenchthe blown polymer by means of latent heat of vaporization of the blowingagent and Joul-Thomson effect by the gas generated by the blowing agentthereby to fix the molecular orientation.

The most important features of this invention thus reside in the use asthe blowing agent of water which has a large expansion capacity and hasa large latent heat of vaporization; the improvement in dispersion ofthe water finely in the polymer mass by the use of a water-sorptionagent; and the improvement is wettability at the surface of the waterand the polymer by the use of a surface active agent.

According to this invention, briefly summarized, there is provided aprocess for producing fine fibrous structures wherein an aqueousdisperse system comprising a molten linear polymer containing a finewatersorption agent and a positive solvent with respectto the polymer isejected from a high-pressure region at a temperature above the meltingpoint of the polymer and below the critical temperature of the dispersesystem and at a pressure above the saturated vapor pressure of thedisperse system into a low-pressure region at a temperature and pressureconducive to evaporation of a liquid phase within the disperse systemthereby to produce a fine fibrous structure of the polymer.

The nature, principle, utility, and further features of the inventionwill be apparent from the following detailed description beginning witha consideration of general aspects of the invention and concluding withspecific examples of practice illustrating preferred embodiments of theinvention.

DETAILED DESCRIPTION In accordance with this invention, as mentionedhereinabove, an aqueous disperse system is used as a spinning solutionof the linear polymer to be spun by ejection into a low-pressure region.The droplets or particles of the polymer within the aqueous dispersesystem contain a fine water-soluble or water-adsorptive orwater-absorptive material, that is, a water-sorption agent. Since thedroplets of molten polymer contain a hydrophilic substance of thisnature within an aqueous disperse system, these droplets containtherewithin a substantial quantity of water.

7 Accordingly, by the practice of this invention, the followingdesirable effects and results are afforded.

1. Blowing effect The blowing effect of the water contained within thepolymer droplets is utilized. More specifically, when the aqueousdisperse system is ejected into the lowpressure region, the pressure onthis water within the droplets is abruptly released, whereby this watervaporizes instantaneously and exhibits a blowing effect. This abruptpressure release is accompanied by a rapid cooling effect (Joule-Thomsoneffect and latent heat of vaporization), whereby the molten polymer iscooled simultaneously with its blowing action.

- The water within the molten polymer fluid droplets may be broadlyclassified into two kinds as distinguished by their states of existence.That is, the first kind is water with a water-sorption agent as itscenter which exists as a dispersed phase within a continuous phase ofthe molten polymer, while the second kind is the water corresponding tothe case where this dispersed phase has consolidated considerably andbecome communicative with the outer side of the polymer droplets. Theblowing effect is particularly pronounced with the former kind of water,that is, the water which is enveloped by the walls of the moltenpolymer.

- In the case where a positive solvent with respect to the polymer isused in the preparation of the aqueous disperse system of the polymer, afurther blowing effect can be expected also from the evaporation in thelowpressure region of the positive solvent which has infiltrated intothe interior of the polymer fluid droplets.

2. Molecular orientation effect Two kinds of water exist in this polymerdisperse system, namely, water which has infiltrated into the interiorof the above mentioned polymer droplets and water 'which has not soinfiltrated and is present outside of the droplets.

The latter water evaporates at the instant when the disperse system isextruded or ejected into the lowpressure region and becomes a stream ofwater vapor, which advances with extremely high energy in the ejectiondirection. This stream of water vapor exerts a great stretching actionon the polymer in the ejection or spinning direction.

Since the quantity of the former water becomes considerable inaccordance with this invention, the contribution of the evaporation ofthis water to the stretching action also amounts to a considerabledegree.

The abrupt evaporation of the water (and positive solvent) inside andoutside of the polymer droplets as described above also gives rise to arapid cooling of the interior and exterior of the polymer, whichthereupon solidifies. These blowing, stretching, and cooling actionstake place substantially simultaneously, whereby a structure comprisingfine fibers which has a highly orientated structure and, moreover, ishighly fibrillated is produced.

The degree of orientation and stiffness of these fine fibers differ withwhether or not the water enclosed within the molten polymer droplets isexisting as a dispersed phase within the continuous phase of the moltenpolymer. More specifically, in the former case, the contribution towardpolymer stretching due to the evaporation and expansion of the enclosedwater is great, whereby fine fibers of high orientation and highstiffness are produced. Accordingly, beating is facilitated, and,moreover, the stiffness of a synthetic paper made from these fibers iscomparable to that of a natural pulp paper.

On the other hand, in the latter case wherein the water enclosed withinthe polymer droplets is not existing as a dispersed phase, the enclosedwater is commuand the orientation of the polymer due to the stretchingaction of the water outside of the polymer droplets becomes predominant.

Consequently, the degree of orientation of the resulting fine fibers issomewhat lower than that in the former case, but synthetic papers madewith these fibers are highly useful depending on the use, such as, forexample, uses where pliability and softness are required and uses asdisposables.

3. Reduction of quantity of solvent used For the spinning solution inthe practice of this invention, a solution of the polymer in an organicsolvent is not used, and the polymer droplets within the intendedaqueous disperse system of emulsive liquid moreover, are not in the formof a solution of the polymer but are in molten state. Accordingly, insuch a mode of utilization of the polymer, a solvent is not absolutelynecessary.

According to this invention, however, a positive solvent with respect tothe polymer used is used for the purposes of facilitating thepreparation of the aqueous disperse system and facilitating theinfiltration of water into the fine water-sorption agent within thepolymer droplets in the disperse system.

In view of these purposes of use of a solvent, the quantity used thereofis remarkably small, being less than percent, preferably less than 50percent and ordinarily less than 30 percent, of the weight of thepolymer used.

As mentioned hereinabove, this invention contemplates the use of amolten substance in the form of fluid droplets of the polymer instead ofa solution of the polymer. However, the coexistence, albeit in a smallquantity, of a positive solvent in the high-pressure region underhigh-temperature and high-pressure conditions gives rise to thepossibility of the existence of the polymer within the liquid dropletsin a swollen state or the form of a solution to some extent.Accordingly, according to this invention the term polymer droplets isintended to include the case of a solution of the polymer.

4. Extension of the range of usable solvents By the conventionalspinning process wherein a spinning solution is ejected into alow-pressure region, it has not been feasible to use a solvent of highboiling point because of difficulties relating to the blowing force andthe removal of residual solvent.

By the practice of this invention, however, highboiling-point solventscan also be used. Even if a highboiling-point solvent remains within theproduct polymer, it can removed with relative ease by washing theproduct with water containing an emulsifier. The emulsified liquidcontaining a small quantity of the solvent and formed during thiswashing can be effectively utilized as a starting material for thepreparation of a polymer emulsive liquid.

5. I-Iydrophilic property In accordance with a preferred embodiment ofthis invention, an emulsifier is used for preparing a stable polymerdisperse system.

This emulsifier and the water-sorption material used remains within thepolymer even when water evaporates in the low-pressure region.Accordingly, the fine fibrous structure obtained in this case hasexcellent hydrophilic property and has ample water-dispersibility evenwithout the addition of a dispersing agent. Furthermore, this fibrousstructure is not accompanied by problems such as foaming and can bereadily sent to the succeeding process ste'ps ofmacerating orrbeatingand paper making. Furthermore,-the fibersof this fibrous structure canbe used to makesynthetic papers having excellent fwater wettabilitywhich was unattainable in the prior art.

1. MaterialszLinear Polyme For the polymer to be used in accordance withthis invention, any linear polymer capable of forming fibers can beused.:For full utilization of the molecular orientation effect, acrystalline polymer is desirable. Furthermore, in view of the fact thatthis polymer is mostly placed in the state of an aqueous disperse systemunder pressurize and heated conditions, and in consideration ofhydrolysis which may occur, it may be said, if a choice is to be made,that a polymer produced by polyaddition is preferable to a polymerproduced by polycondensation.

Examples of such linear polymers are polyolefin resins,polychloroethylene resins, polyvinyl aromatic resins, polyamide resins,polyester resins, polyimide resins, and polycarbonate resins, ashomopolymers and copolymer. Of these, polyolefin resins such ashomopolymers of ethylene, propylene, and butenel; copolymers of at leasttwo of the monomers of ethylene, propylene and butene-l such asethylene-propylene copolymers; copolymers, wherein said monomer ormonomers are predominant constituents, of said monomers with-othermonomers copolymerized therewith such as ethylenevinylacetatecopolymers, ethylene-acrylate copolymers; and mixtures of said polymers,are representative, and among these, isotactic polypropylenes andhigh-density polyethylenes are most typical. These polymers can be usedsingly or as mixtures thereof. Water-sorption agent Another importantfeature of this invention is the fine watersorption agent caused toexist within the droplets of the molten polymer in the aqueous dispersesystem.

The water-sorption agents usable according to this invention may bebroadly classified into water-soluble materials a) and materials b)which are difficult to dissolve or are insoluble in water and whichsorb, namely adsorb or absorb, water. These agents may be materialswhich decompose when they contact water which has infiltrated into thedroplets of the molten polymer in the high-pressure region.

a. Water-soluble materials Inorganic compunds and organic compunds whichdissolve in water or which dissolve water in the highpressure region areusable.

Specific examples of usable water-soluble materials are inorganicmaterials such as nitrates, acetates, sulfates, sulfites, carbonates,phosphates, hydroxides, and halides of alkali metals, alkaline earthmetals, and ammonium and complex salts or double salts thereof, as, forexample, NaNO CH COONa, MgSO Na CO NaH PO NaOI-I, NaCl, and (NH Al (S00and organic water-soluble materials such as CMC, starch, gum arabic,agar, polyacrylamide, polyacrylic acid or Na salt thereof, polyethyleneimine, polyethylene oxide, polyvinyl pyrrolidone, and polyvinylalcohols. While liquid materials such as ethylene glycol and glycerineare also effective,it is difficult to blend these substances to a highconcentration.

Of these compounds, particularly salts-having water of crystallizationas, for'example, MgSO .7I-l 0, Nag. SO .IOH O, and Na SO. ,.7I-I O,exhibit pronounced effectiveness in forming fine fibers. Thetransformation of the polymer into fine fibers is accomplished by theexpansion of the water enclosed within the polymer droplets and by thestretching effect of the water outside of the droplets, as mentionedhereinbefore. The

splitting force of the polymer droplets when a salt having water ofcrystallization is used is equal to the splitting force of an expandingorganic solvent in the case where a solution of the polymer in theorganic solvent is spun by ejection into a low-pressure region.

That is, one percent by volume of the water within the polymer dropletsin the process of this invention corresponds to one percent by volume ofthe solvent in the process wherein an organic solvent solution ofpolymer is used. Thus, by the practice of this invention, the sameeffectiveness in forming fine fibers as in the conventional method offlash spinning a polymer solution through the use of an organic solventof lower boiling point than water is attained. This is an importantfeature of this invention.

b. Water-insoluble material Inorganic materials and organic materialswhich, although incapable of being dissolved in water or of dissolvingwater in the high-pressure region, adsorb or absorb water. I

In this case, since the quantity of the water enclosed within thepolymer droplets is small, the splitting effect decreases somewhat, butthe fibrilation in the beating process step is facilitated by thematerial remaining in the fine fibers. Accordingly, the fine fibersfinally obtained are identical to five fibers obtained by blending awater-soluble material.

Specific examples of usable water-insoluble materials are inorganic andorganic fillers such as calcium carbonate, water-insoluble solidscomprising silicates such as clays (Kaoline, Pyrophyllite), white carbon(or silica amorphous), talc Mica, Fuller earth, and diatomaceous earth(or siliceous marl), basic magnesium carbonate, cellulose powder andpulp, and hydrates which are difficult to dissolve in water such asmagnesium oxalate and magnesium phosphate. For sorption of water inlarge quantity, porous substances are particularly effective.

Positive solvent In order to disperse the linear polymer in a stablemanner as fluid droplets in molten state in a water phase and, moreover,to facilitate the infiltration of water into the fine water-sorptionagent within the polymer droplets in the aqueous disperse system, asolvent, more specifically, a positive solvent, is preferably used.

The term positive solvent is herein used to designate a solvent in whichthe given molten polymer is at least partially soluble under thetemperature and pressure conditions of the high-pressure region.Accordingly, this solvent may or may not have a positive characteristicof this nature in the low-pressure region or under the conditions ofroom temperature and atmospheric pressure. In general, however, thissolvent is probably capable of causing the given solid polymer to atleast swell at least under heating.

Solvents capable of promoting the infiltration of water (and anemulsifier) into the droplets of molten polymer are all usable. Forexample, with polyolefin polymers, aliphatic hydrocarbons, alicyclichydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and thelike, such as, for example, n-pentane, n-

hexane, n-heptane, cyclopentane, cyclohexane, dichloromethane, benzene,toluene, xylenes, decalin, tetralin, napthalene, are used singly or asmixtures.

In accordance with a preferred mode of practice of this invention, theaqueous disperse system is an aqueous emulsive liquid or aqueousemulsion of molten polymer prepared by the use of an emulsifier. Anyemulsifier is usable provided that it is capable of forming a stableemulsive liquid in the high-pressure region. Accordingly, a suitableemulsifier may be selected from those generally sold on the market.

Specific examples of suitable emulsifiers are nonionic, anionic,cationic, amphoteric, and surfactants used singly or as mixtures.

In the resulting aqueous emulsive liquid or aqueous emulsion of polymer,the polymer may be present in the form of fine particles or of larger oragglomerated particles.

2. Polymer aqueous disperse system In the practice of this invention,use is made of a special polymer aqueous disperse system. Morespecifically, the droplets of the molten polymer contain a finewater-sorption agent, which makes possible the enclosure of watertherewithin.

As mentioned hereinbefore, this enclosed water exists as a dispersedphase within the continuous phase of molten polymer or exists in a statewherein it is communicating with the outside of the polymer dropletsbecause of the consolidation of this dispersed phase. Whichever statethis enclosed water assumes is determined by the quantity of theenclosed water. On one hand, this quantity of the enclosed water isdetermined by the quantity of the water-sorption agent within thepolymer droplets.

More specifically, when the (water water-sorption agent) content withinthe droplets is up to the order of approximately 60 percent, the formerstate is assumed, and the enclosed water exists as independent cells.When this content exceeds approximately 60 percent and is of a value upto approximately 80 percent, the enclosed water exists in the latterstate.

The lower limit of the content of the water-sorption agent isapproximately 20 percent, preferably approximately 30 percent. The abovestated percentages are by weight. While this enclosed water is composedprincipally of water, it ordinarily contains the watersorption agent andthe emulsifier.

The aqueous dispersion of molten polymer of this character can beprepared, in general, by any method by which the desired disperse systemcan be prepared. That is, it is desirable to make a stable dispersesystem and, moreover, to prepare it in the form of an aqueous emulsiveliquid by using an emulsifier and a positive solvent relative to thepolymer thereby to facilitate the infiltration of water into thedroplets of molten polymer.

Examples of suitable methods for preparing the aqueous disperse systemof the molten polymer are set forth below.

1. Preparatory forming method l.l Preparatory mixing First, the polymerand the water-sorption agent are uniformly blended beforehand by anordinary method wherein additives such as a pigment, a filler, astablizer against oxidation, an antistatic agent, and a reinforcingagent are blended with a thermoplastic polymer. For

this blending, a mixing machine such as an extruder, kneader, rolls, aBanbury mixer, and a co-kneader is used.

While the polymer blend after mixing may be in the state of lumps,granules, fine powder, and other forms, it is preferably in a finepowder form of an average particle diameter of from 50 to 300 microns.If the particles are made excessively fine, however, the droppingoutphenomenon of the mixed materials will tend to become remarkable,whereby care must be exercised with respect to this tendency.

Blending with the solvent is also effective particularly for elevatingthe degree of mixing. Furthermore, as a special mixing method thewater-sorption agent and the fine polymer powder to be mixed may beformed in a semi-molten state under a.high pressure into a lumpysubstance.

1.2 Forming the aqueous disperse system The polymer blend after mixingis caused to be suspended in an emulsive liquid prepared by emulsifyinga small quantity of a positive solvent in water. The suspension thusformed is heated to a temperature above the melting point of the polymerand subjected to a pressure above the critical pressure of this emulsiveliquid system.

The action of the solvent and the emulsifier causes water to infiltrateinto the interior of the polymer droplets and to dissolve the admixedwater-sorption agent or be adsorbed on the water-sorption agent to becaptured within the polymer. In addition, with this water as a nucleus,a portion of the water is caused by the positive solvent and theemulsifier to penetrate into the interior of the polymer droplets.

In this manner, water is a quantity corresponding to the volume orsorbed quantity of the admixed watersorption agent and the quantity ofinfiltration due to the action of the positive solvent and emulsifier isheld within the polymer droplets.

Particularly in the case of a blend of the polymer in the state of afine powder, the molten polymer undergoes recombination enclosing excesswater existing on the outer peripheral surface, whereby polymer dropletsare formed. Furthermore, the capillaries produced at the time of waterinfiltration are closed by variations in the system conditions such aspressure and temperature, whereby independent cells can be formed.

2. Direct forming method In this method, the enclosure of water andwatersorption agent existing at the outer periphery due to mutualrefusion of polymers is utilized.

A water-sorption agent which isdifficult to dissolve in water and apolymer powder are suspended in an emulsive liquid comprising water, apositive solvent, and an emulsifier, and the resulting suspension isheated and pressurized to a high temperature above the melting point ofthe polymer and above the saturated vapor pressure of the emulsiveliquid.

A small quantity of the water is caused by the action of the positivesolvent and emulsifier in the emulsive liquid to infiltrate into theinterior of the polymer droplets. At a temperature above its meltingpoint, the polymer undergoes coupling in a state wherein it is enclosingwater and the water-sorption agent existing at the outer peripheries ofthe fine polymer particles, whereby an aqueous disperse system of moltenpolymer in a state similar to that in the case (1.1) where preparatorymixing is carried out. In the instant case, the finer and more porousthe polymer powder is, the better is the resulting droplet structure,i.e., the formation of the enclosed water cells.

In all of the above described methods, pigments, reinforcing agents,stabilizers, and other additives for polymers may be added to thepolymer. Furthermore, this polymer aqueous disperse system may containother auxiliary ingredients depending on the necessity. For example, inaddition to the above mentioned emulsifier, water-solublesalts,water-soluble polymers, and other additives can be added for the purposeof adjusting characteristics such as the viscosity and the stability ofthe emulsive liquid and for other purposes. The water-soluble polymerscan be removed by washing from the resulting fine fibrous structures orrendered insoluble in water.

Furthermore, other materials such as fine fillers and blowing agents canbe added. In the case where this disperse system is an'aqueoussuspension, a suspension stabilizer can be used.

The composition of this aqueous disperse system of a polymer ispreferably as follows. The polymer concentration within the dispersesystem is from to 70 percent, preferably from 20 to 30 percent. Thequantity of the water-sorption agent relative to that of the polymer isfrom 20 to 80 percent, preferably from 30 to 50 percent. The quantity ofthe positive solvent relative to that of the, polymer is greater thanzero percent and of a value less than 100 percent, preferably less than50 percent and ordinarily less than 30 percent. The above statedpercentages are all by weight. When an emulsifier is used, its contentin the aqueous disperse system (emulsive liquid) of the polymer is ofthe order of less than a number of percent.

3. Spinning The high-pressure region in which the above describedaqueous disperse system of the molten polymer initially exists should beat a temperature sufficient for the existence therein of the polymer asdroplets in molten state. Furthermore, since this aqueous dispersesystem should exist as a disperse system, this temperature should bebelow the critical temperature of the disperse system, and, at the sametime, the pressure of the region should be at a value above thesaturated vapor 3 pressure of the water (and solvent) at thattemperature.

Since the blowing action of water is principally utilized in thepractice of this invention, the temperature and pressure conditions ofthe high-pressure region are selected with consideration of theirrelationships with the pressure and temperature conditions of thelow-pressure region. Accordingly, in the case where the low-pressureregion is at atmospheric pressure, for example, the blowing action ofthe water does not become sufficient at a temperature of thehighpressure region of less than 130C.

In order to apply or sustain this pressure condition in thehigh-pressure region, any pressure-applying means can be used. However,the ordinary measure is to introduce a pressurized gas, which ispreferably inert with respect to the disperse system. One example of theconditions of the high-pressure region is that wherein, in the casewhere an aqueous emulsive liquid of high-density polyethylene orpolypropylene is to be ejected into a low-pressure region at roomtemperature and atmospheric pressure, fine fibers which can be used tomake paper can be produced at a temperature I of the order of from 180to 200C and at a pressure of the order of from 50 to 60 kg/cm Theextrusion or ejection of the aqueous emulsive liquid of the polymer fromthe high-pressure region to the low-pressure region may be carried outthrough an ejection orifice device which has a single orifice, aplurality of orifices, or orifices of slit shape or some other shape. Wehave found that, while an ejection velocity from theejection orificedevice is preferably above the velocity of sound (330 meters/second), avelocity of approximately one half of the velocity of sound or lowervelocity may be used.

While the low-pressure region is ordinarily at atmospheric pressure androom temperature, it is also possible to maintain this region underreduced pressure and heated conditions in order to promote theevaporation of the liquid phase, particularly water, within the emulsiveliquid.

4. Product The fine fibrous structure thus obtained is dried directly asit is or is washed with an aqueous solution of an emulsifier and thendried, whereupon the objective product is obtained.

This fine fibrous structure can be utilized as an openmesh or networkstructure, or by macerating or beating this fine fibrous structure by adry or wet process, it can be also utilized as a staple fiber or as astarting material for paper making. According to a preferred embodimentof this invention, as mentioned hereinbefore, there are provided finefibers of good hydrophilic characteristic which are particularlysuitable for use as a starting material for paper making and, moreover,has excellent compatibility with natural cellulosic pulp.

In order to indicate still more fully the nature and utility of thisinvention, the following specific examples of practice constitutingpreferred embodiments of the invention and results are set forth, itbeing understood that these examples are presented as illustrative only,and that they are not intended to limit the scope of the invention.

EXAMPLE 1 Fifty parts of linear polyethylene of a melt index, MI, of 5and a density of 0.965 gram/cc. in powder form and 50 parts of magnesiumsulfate dried for 4 hours at a temperature of from to C and passingthrough a 40-mesh sieve were blended in a roll blender operated with aroll surface temperature of C. The mixture thus blended was pelletized,and then the pellets were pulverized into a powder in a mill.

Separately, one part of a non-ionic emulsifier of a HLB 18 was dissolvedin 83 parts of water, and then one part of n-pentane was added to theresulting solution to prepare a homogeneous emulsive liquid. To thisliquid, 15 parts of the above described powder of the blend was addedand uniformly dispersed, whereupon an aqueous mixture was obtained.

This aqueous mixture was placed in a sealed vessel, the interiorpressure of which was increased to 40 kg/cm with pressurized nitrogen.Then,as the mixture was agitated, it was heated to and at C. After 50minutes, the pressure within the vessel rose to 53 kg/cm because of theheating. The interior of the sealed vessel was communicative through agate valve to a slit nozzle of a width of 0.5 mm. and a length of 10After 50 minutes, the system pressure was further increased withpressurized nitrogen to 70 kg/cm and the gate valve was abruptly openedto eject the system mixture into the atmosphere. As a result, a mass ofa fine fiber having a highly orientated structure was obtained.

EXAMPLE 2 Fifteen parts of a linear polyethylene of MI of and a densityof 0.965 gram/cc. was dissolved at a temperature of from 120 to 140C in70 parts of xylene. To the resulting solution, parts of sodium chloridedried for 4 hours at a temperature of from 160 to 170C and passingthrough a -mesh sieve was added while the solution was vigorouslyagitated.

After thorough agitation, the resulting mixture was poured graduallyinto methyl alcohol to cause a blend of the polyethylene and sodiumchloride to precipitate. This precipitate was lightly pulverized in amixer to obtain a blend in powder form, which was then washed from 2 to3 times with methyl alcohol to remove the xylene. The resulting mass wasthen dried at 60C for 24 hours for complete removal of the solvents.

15 parts of the blend thus obtained was added to an emulsive liquidcomprising 81 parts of water, 3 parts of n-pentane, and 1 part of anon-ionic emulsifier of a HLB 14 thereby to form an aqueous mixture,which was then process in accordance with the procedure set forth inExample 1. As a result a three-eimensional net orientation was produced.

EXAMPLE 3 Fifty parts of a linear polyethylene of a Ml of 5 and adensity of 0.965 gram/cc. and parts of a clay dried for 4 hours at atemperature of from 160 to 170C and consisting of particles of anaverage diameter of 5 microns were blended in a roll blender and thenpulver ized.

15 parts of the resulting blend was added to an emulsive liquidcomprising 81 parts of water, 3 parts of npentane, and one part of anon-ionic emulsifier of a HLB 14 to form an aqueous mixture, which wasprocessed according to the procedure specified in Example 1. As aresult, a fine fibrous structure was produced.

EXAMPLE 4 Fifty parts of an isotactic polypropylene of a MI of 9 inpowder form and 50 parts of magnesium sulfate dried for 4 hours at atemperature of from 160 to 170C and passing through a 40-mesh sieve wereblended by means of a roll blender operated with a roll surfacetemperature of 210C. The mixture thus blended was pelletized and thenpulverized into a powder in a mill.

Separately, a homogeneous emulsive liquid was prepared by dissolving onepart of a non-ionic emulsifier of a HLB 18 in 83 parts of water and thenadding one part of heptane to the resulting solution.

To this emulsive liquid, 15 parts of the above described blended powderwas added to form an aqueous mixture, which was then processed for 50minutes in an autoclave at 180C and 50 kg/cm pressure and then ejectedinto the atmosphere. As a result, a fine fibrous structure havingstiffness was produced.

EXAMPLE 5 Seventy parts of Nylon-6 and 30 parts of sodium sulfite driedfor 4 hours at a temperature of from to C were granulated at a maximumtemperature of 270C by means of a 45 mm d) extruder, and then theresulting granules were pulverized.

Separately, a homogeneous emulsive liquid was prepared by dissolving onepart of an anionic surfactant of a HLB 18 in 83.5 parts of water andthen adding 0.5 part of cresol to the resulting solution.

In this emulsive liquid, 15 parts of the above described powder wasuniformly dispersed to form an aqueous mixture. This mixture was placedin a sealed vessel, the interior pressure of which was increased withpressurized nitrogen to 40 kg/cm and the aqueous mixture was heated toand at 240C as it was agitated.

After 60 minutes, the pressure within the vessel had increased to 65kg/cm at which point a discharge valve of the vessel was abruptly openedto eject the aqueous emulsive liquid of the polymer into the atmosphere.As a result, fine fibers having a highly orientated and fibrillatedstructure of substantial stiffness were produced.

EXAMPLE 6 Fifteen parts of the blended mixture of a polyethylene andmagnesium sulfate prepared according to Example l was added to asolution prepared by dissolving one part of an anionic surface-activeemulsifier of a HLB 12 in 84 parts of water thereby to form an aqueousmixture in which the blended mixture was uniformly dispersed.

This aqueous mixture was placed in a sealed vessel, and the pressurewithin the vessel was increased with pressurized nitrogen to 45 kg/cmThe aqueous mixture was then heated to and at 180C as it was agitated.After 120 minutes, the vessel interior pressure had risen to 55 kg/cm atwhich point a discharge valve of the vessel was opened to discharge thepolymer aqueous emulsive liquid into the atmosphere. As a result, afoamed structure having as a major part, uniform cells foamed from 5 to10 times and, as one part, fine fibers having a fibrillated structure.

EXAMPLE 7 A homogeneous aqueous suspension was prepared by dissolving 2parts of an anionic surface-active emulsifier of a HLB 18 in 35 partswater and adding to the resulting solution 25 parts of calcium carbonateand 40 parts of an isotactic polypropylene of a Ml of 5 in pelletizedform. r

, This suspension was placed in a sealed vessel and, after the pressurewithin the vessel was raised to 45 kg/cm with pressurized nitrogen, washeated to and at 180C under agitation. After 120 minutes, the pressurewithin the vessel had increase to 55 kg/cm at which point, a dischargevalve of the vessel was opened to discharge the suspension into theatmosphere. As a result, fine fibershaveing a fibrillated structure andstiffness were produced.

We claim:

1. A process for producing fine fibrous structures which comprises thesteps of:

l. preparing a heterogeneous aqueous dispersion system comprising amolten polyolefin dispersed therein in a quantity of from 5 to 70percent by weight of the aqueous dispersion system, water, and asubstantially water-immiscible positive solvent for the polymer, saidmolten polyolefin containing water and a fine water-sorption agent whichis inherently solid in a quantity of from 20 to 80 percent by weight ofthe polyolefin; said positive solvent being in a quantity of less than50% by weight of the polymer, at least a part of which is present withinthe molten polyolefin, and

2. passing said aqueous dispersion system from a high-pressure region ata temperature above the melting point of the polymer and below thecritical temperature of said aqueous dispersion system and at a pressureabove the saturated vapor pressure of said system into a low-pressureregion at a temperature and pressure at which the liquid phase withinthe dispersion system can evaporate thereby to produce a fine fibrousstructure of the polymer.

2. A process according to claim 1, wherein the positive solvent isselected from the group consisting of npentane, n-hexane, n-heptane,cyclopentane, cyclohexane, dichloromethane, benzene, toluene, xylenes,decalin, tetralin, naphthalene, and mixtures thereof.

3. A process according to claim 1 wherein the positive solvent ispresent in a quantity of less than 30% by weight of the polymer.

4. A process according to claim 1 wherein the molten polyolefin isselected from the group consisting of high density polyethylene and highdensity polypropylene and the heterogeneous aqueous dispersion system ispassed from a high pressure region in which the pressure range isbetween 50 to 60 kg/cm and the temperature is between 180 to 200C to alow pressure region in which the pressure is atmospheric pressure andthe temperature is room temperature.

5. A process for producing fine fibrous structures as claimed in claim 1in which the aqueous disperse system is an aqueous emulsive liquid.

6. A process for producing fine fibrous structures as claimed in claim 1in which the water-sorption agent is a fine solid of a member selectedfrom the group consisting of nitrates, oxalates, acetates, sulfates,sulfites, carbonates, phosphates, hydroxides, and halides of alkalimetals, alkaline earth metals (including magnesium) and ammonium, andmixtures thereof.

7. A process for producing fine fibrous structures as claimed in claim 1in which the water-sorption agent is a water-insoluble silicate.

8. A process for producing fine fibrous structures as claimed in claim 1in which the aqueous dispersion system is prepared by blending the finewater-sorption agent with the polymer in a molten or solution state,suspending the resulting blend in an aqueous emulsion, and heating andpressurizing the resulting suspension to and at a temperature above themelting point of the polymer and a pressure above the critical pressure(Saturated Vapour Pressure) of the suspension.

9. A process for producing fine fibrous structures as claimed in claim 1in which the aqueous dispersion system is prepared by suspending a finewater-sorption agent which substantially does not dissolve in water andthe polymer in powder form in an aqueous emulsion of the positivesolvent and heating and pressurizing the resulting suspension to and ata temperature above the melting point of the polymer and a pressureabove the critical pressure of the suspension.

10. A process for producing fine fibrous structures as claimed in claim1 in which the polyolefin is a member selected from the group consistingof homopolymers of ethylene, propylene, and butene-l; copolymers of atleast two of the monomers ethylene, propylene, and butene-l; copolymers,wherein said monomers are predominant constituents, of said monomerswith other monomers co-polymerizable therewith; and mixtures of saidpolymers.

1 l. A process for producing fine fibrous structures as claimed in claim1 in which the concentration of the polyolefin in the dispersion systemis from 5 to percent by weight relative to the quantity of the dispersesystem.

12. A process for producing fine fibrous structures as claimed in claim1 in which the polyolefin is a member selected from the group consistingof polyethylenes, isotactic polypropylenes, and mixtures thereof, andthe positive solvent is a member selected from the group consisting ofaliphatic hydrocarbons, alicyclic hydrocarbons, and aromatichydrocarbons.

13. A process for producing fine fibrous structures as claimed in claim12 in which the aqueous dispersion system is prepared through. the useof a surfactant selected from the group consisting of nonionicsurfactants and anionic surfactants, said surfactants beingwater-soluble and capable of forming an emulsive liquid in the highpressure region.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,914,354 Dated October 21,1975

Inventor(s) Shiro Ueki et a1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

First (title) page, Col. 1, in the line designated [73] relating to theassignee's name,

change "Oki" to Oji Signed and Scaled this ninth Day of March 1976[SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner nfParentsand Trademarks

1. A PROCESS FOR PRODUCING FINE FIBROUS STRUCTURES WHICH COMPRISES THESTEPS OF:
 1. PREPARING A HETEROGENEOUS AQUEOUS DISPERSION SYSTEMCOMPRISING A MOLTEN POLYOLEFIN DISPERSED THEREIN IN A QUANITY OF FROM 5TO 70 PERCENT BY WEIGHT OF THE AQUEOUS DISPERSION SYSTEM, WATER, AND ASUBSTANTIALLY WATER-IMMISCIBLE POSITIVE SOLVENT FOR THE POLYMER, SAIDMOLTEN POLYOLEFIN CONTAINING WATER AND A FINE WATER-SORPTION AGENT WHICHIS INHERENTLY SOLID IN QUANTITY OF FROM 20 TO 80 PERCENT BY WEIGHT OFTHE POLYOLEFIN, SAID POSITIVE SOLVENT BEING IN A QUANITY OF LESS THAN50% BY WEIGHT OF THE POLYMER, AT LEAST A PART OF WHICH IS PRESENT WITHINTHE MOLTEN POLYOLEFIN, AND
 2. PASSING SAID AQUEOUS DISPERSION SYSTEMFROM A HIGH-PRESSURE REGION AT A TEMPERATURE ABOVE THE MELTING POINT OFTHE POLYMER AND BELOW THE CRITICAL TEMPERATURE OF SAID AQUEOUSDISPERSION SYSTEM AND AT A PRESSURE ABOVE THE SATURATED VAPOR PRESSUREOF SAID SYSTEM INTO A LOW-PRESSURE REGION AT A TEMPERATURE AND PRESSUREAT WHICH THE LIQUID PHASE WITHIN THE DISPERSION SYSTEM CAN EVAPORATETHEREBY TO PRODUCE A FINE FIBROUS STRUCTURE OF THE POLYMER.
 2. passingsaid aqueous dispersion system from a high-pressure region at atemperature above the melting point of the polymer and below thecritical temperature of said aqueous dispersion system and at a pressureabove the saturated vapor pressure of said system into a low-pressureregion at a temperature and pressure at which the liquid phase withinthe dispersion system can evaporate thereby to produce a fine fibrousstructure of the polymer.
 2. A process according to claim 1, wherein thepositive solvent is selected from the group consisting of n-pentane,n-hexane, n-heptane, cyclopentane, cyclohexane, dichloromethane,benzene, toluene, xylenes, decalin, tetralin, naphthalene, and mixturesthereof.
 3. A process according to claim 1 wherein the positive solventis present in a quantity of less than 30% by weight of the polymer.
 4. Aprocess according to claim 1 wherein the molten polyolefin is selectedfrom the group consisting of high density polyethylEne and high densitypolypropylene and the heterogeneous aqueous dispersion system is passedfrom a high pressure region in which the pressure range is between 50 to60 kg/cm2 and the temperature is between 180* to 200*C to a low pressureregion in which the pressure is atmospheric pressure and the temperatureis room temperature.
 5. A process for producing fine fibrous structuresas claimed in claim 1 in which the aqueous disperse system is an aqueousemulsive liquid.
 6. A process for producing fine fibrous structures asclaimed in claim 1 in which the water-sorption agent is a fine solid ofa member selected from the group consisting of nitrates, oxalates,acetates, sulfates, sulfites, carbonates, phosphates, hydroxides, andhalides of alkali metals, alkaline earth metals (including magnesium)and ammonium, and mixtures thereof.
 7. A process for producing finefibrous structures as claimed in claim 1 in which the water-sorptionagent is a water-insoluble silicate.
 8. A process for producing finefibrous structures as claimed in claim 1 in which the aqueous dispersionsystem is prepared by blending the fine water-sorption agent with thepolymer in a molten or solution state, suspending the resulting blend inan aqueous emulsion, and heating and pressurizing the resultingsuspension to and at a temperature above the melting point of thepolymer and a pressure above the critical pressure (Saturated VapourPressure) of the suspension.
 9. A process for producing fine fibrousstructures as claimed in claim 1 in which the aqueous dispersion systemis prepared by suspending a fine water-sorption agent whichsubstantially does not dissolve in water and the polymer in powder formin an aqueous emulsion of the positive solvent and heating andpressurizing the resulting suspension to and at a temperature above themelting point of the polymer and a pressure above the critical pressureof the suspension.
 10. A process for producing fine fibrous structuresas claimed in claim 1 in which the polyolefin is a member selected fromthe group consisting of homopolymers of ethylene, propylene, andbutene-1; copolymers of at least two of the monomers ethylene,propylene, and butene-1; copolymers, wherein said monomers arepredominant constituents, of said monomers with other monomersco-polymerizable therewith; and mixtures of said polymers.
 11. A processfor producing fine fibrous structures as claimed in claim 1 in which theconcentration of the polyolefin in the dispersion system is from 5 to 70percent by weight relative to the quantity of the disperse system.
 12. Aprocess for producing fine fibrous structures as claimed in claim 1 inwhich the polyolefin is a member selected from the group consisting ofpolyethylenes, isotactic polypropylenes, and mixtures thereof, and thepositive solvent is a member selected from the group consisting ofaliphatic hydrocarbons, alicyclic hydrocarbons, and aromatichydrocarbons.
 13. A process for producing fine fibrous structures asclaimed in claim 12 in which the aqueous dispersion system is preparedthrough the use of a surfactant selected from the group consisting ofnonionic surfactants and anionic surfactants, said surfactants beingwater-soluble and capable of forming an emulsive liquid in the highpressure region.